Accurately sizing and precisely locating pressure-sensitive components, such as unprinted or printed labels, conductive components, insulating components, and other similar items, on the surface of a product to which they are to be adhered requires that the component (a) be manufactured to predefined dimensional tolerances, (b) contain a layer of material that adheres the item to the desired surface upon contact, (c) be precisely positioned relative to a transport means, (d) be rigidly attached to the transport means in a precisely defined location, (e) be transported to the desired location on the product surface, and (f) be applied thereto. Of these five requirements, the two that are most difficult to achieve are precise placement and attachment relative to the transport means.
Using labels as an example, one known method for accurately locating and attaching a label to a transport means generally involves stacking individual pre-cut labels into a magazine-type feeding mechanism that precisely positions the labels with reference to the transport means, contacting either the top or bottom label in the stack with the transport means and attaching the label thereto, and transporting the label to the surface to which it is to be applied. The labels placed in the magazine may consist of a single material, such as paper or plastic, to which a layer of adherent material, such as glue or adhesive, must be applied after the label is removed from the magazine and before the label is adhered to the surface, as described in U.S. Pat. No. 4,289,562. Alternatively, the labels may be a composite consisting of a layer of label material and at least one layer of non-adherent material, such as glue or other adhesive, capable of being activated to an adherent state after the label is removed from the stack and before the label is adhered to the desired surface, as described in U.S. Pat. Nos. 3,232,804, 3,232,815, and 3,904,466. Typically, magazine-type feeding devices cannot be used to feed pressure-sensitive labels which contain a pre-activated layer of adherent material that would cause each label in the magazine to adhere to the adjacent label and prevent rapid removal of a single label from the magazine.
Another known and generally used method of accurately locating and attaching a label to a transport means involves partially severing a label from a continuous length of label material, transporting the partially severed label to a precise position relative to the transport means by imparting motion to the unsevered web of the continuous length, attaching the partially severed label rigidly to the transport means, such as by the application of a vacuum, and severing the label completely from the unsevered web by causing the transport means to move relative to the unsevered web. This method is applicable to labels consisting of a single layer to which an adherent layer must subsequently be applied, as described in U.S. Pat. Nos. 4,108,710 and 4,632,721, as well as to labels containing at least one layer of material in the non-adherent state that is capable of being subsequently activated to an adherent state prior to application of the label. This method, as described, cannot be employed for pressure-sensitive label stock containing an exposed adherent layer, since such stock would adhere to any surface of the label application equipment with which it may come into contact thereby preventing unfettered movement of the stock through the equipment.
Precisely locating components containing an adherent layer has long been a problem in packaging, electronics, and general manufacturing operations because of the tendency of the adherent layer to instantly bond to any surface with which it comes into contact. To prevent such adhesion, pressure-sensitive components are normally releasably secured to a continuous carrier strip that prevents the adherent layer of the component from adhering to the surfaces of the equipment in which it is being processed and may also be used transport the component. The carrier strip must be removed prior to adhering the pressure-sensitive component to the surface of the product for which it is intended.
The feedstock employed in most commonly used pressure-sensitive label application equipment generally consists of coils of pre-cut pressure-sensitive labels releasably secured to a continuous carrier strip which maintains the relative position of the pre-cut labels and is additionally used to transport the labels through the label application equipment.
Typically, coils of pre-cut circumferentially severed labels, commonly known as window labels, are prepared by (a) slitting a master coil consisting of a continuous length of pressure-sensitive label stock releasably secured to a continuous length of carrier strip material into multiple narrow strips having a lateral dimension greater than that of the label to be severed therefrom, (b) transporting each narrow strip directly into an integral severing means without intermediate processing, (c) circumferentially severing the pressure-sensitive label stock as the narrow strip longitudinally traverses the severing means such that the carrier strip remains unsevered, and (d) coiling each narrow strip as it exits the severing means.
Because most standard label application equipment guides the carrier stock by remaining in constant contact with one of its longitudinal edges, any uncontrolled variation in the lateral position of a pre-cut pressure-sensitive label relative to the longitudinal edge misaligns the label with respect to the transport means and prevents precise attachment thereto. It is commonly known that uncontrolled variations of from 0.015" to 0.030" in the lateral position of the label on the carrier strip can occur as a result of uncontrolled lateral movement of the aforesaid individual narrow strips upon exiting the slitter and prior to entering the severing means in the label manufacturing process heretofore described. In addition, inconsistencies may also occur in the longitudinal positioning of a pre-cut label relative to the carrier strip due to creep which can take place in the adherent layer of the labels during coiling and storage in the coiled condition. If the adherent layer is of uniform thickness and physical characteristics, the creep normally results in a uniform longitudinal movement relative to the carrier strip. If the adherent layer is non-uniform in thickness or physical characteristics, the relative movement between a pre-cut label and the carrier strip may result in the label being skewed relative to the carrier strip. In either event, the longitudinal variation of the label position relative to the carrier strip precludes precise alignment with the transport means. Standard methods used to locate a circumferentially severed label relative to the transport means, including guiding and transporting the carrier strip by means of accurately located holes along the longitudinal edges of the strip or the use of optical or mechanical means that sense the leading or trailing edge of each label, are generally inadequate to compensate for the aforesaid problems in alignment of the label relative to the transport means.
All of the difficulties enumerated above are compounded when attempting to accurately print a pattern on pre-cut labels, especially when repetitive printing steps are required, as in multi-color printing.
The conventional methods of presenting a pre-cut label to the transport means of label application equipment further compound the problem of precisely locating a label relative to the transport means and, therefore, accurately locating the label on the product surface. Typically, the continuous carrier strip to which pre-cut labels are releasably adhered is passed over a knife edge which alters the direction of movement of the carrier strip such that the label is caused to completely or partially separate from the carrier strip prior to becoming attached to the transport means which may be a vacuum pick-up head attached to either a rotary device or an oscillating pick-and-place device. Upon separating from the label, the carrier stock is subsequently coiled on a driven take-up device.
In one commercially available label application machine, the Cosmos 1 Model 612 produced by Ohio Electronics Machinery, the carrier strip is completely separated from the pre-cut or severed label by reversing the direction of the carrier strip as it moves over a knife edge. The unrestrained label is supported relative to the transport means and directed towards the transport means by a stream of pressurized air directed upwards at the adherent surface of the label. The label is then firmly attached to the transport means by means of a vacuum applied to the transport means. This process fails to provide a means for positively and accurately controlling the location of the label between the moment it separates from the carrier strip and the moment that it attaches to the transport means, thus further exacerbating the difficulty in achieving precise alignment.
One method of partially maintaining positive control of a severed label upon separation from a continuous carrier strip is described in U.S. Pat. No. 3,243,331. In this method, which is used primarily to wrap flag labels circumferentially around small cylindrical products, the leading edge of an adhesive-coated label is peeled from the carrier strip by means of prehensile clamping jaws which clamp onto a minor exposed portion of the label. The clamping jaws peel the label from the carrier strip, transport the label over the surface of the product to which it is to be adhered, and move down to adhere the label to the surface. Although this method assures that a small portion of the label is positively located and restrained during separation from the carrier material and during transport, it does not provide for rigid support of the entire label or even a major portion of the label during separation and transport. Therefore, this method does not assure accurate placement of the label. Further, this method does not provide a means for preventing adherence of the label to the jaws.
U.S. Pat. No. 4,188,251 discloses a low speed method of manually applying a two-part, pre-cut label in which only partial positive control of the label is maintained prior to adhering the label to the desired surface. The two-part label employed in this method consists of a first part that is releasably adhered to a continuous carrier strip and a second part that is devoid of an adherent layer and partially severed from the first part and partially severed to a greater extent from the second part of the adjacent label. In this method, the carrier strip is removed from all but a small portion of the adherent surface of the first label part by drawing the carrier strip around a relatively sharp bend until the label is advanced to a position at which only a trailing marginal end portion remains adhered to the carrier strip. The label is next rigidly adhered to the surface of the product prior to being separated from the carrier strip and finally severed from the adjacent label. Obviously, this method of placing labels on a product surface from a hand-held device does not provide positive control of label placement and cannot be used for the automated manufacture of fully severed labels and the accurate application of the labels to the surface of products at high speeds.
A method of separating a pre-cut label from a continuous carrier strip and applying the label to the moving surface of a product is described in U.S. Pat. No. 4,080,239. In this method, a continuous carrier strip is partially separated from a pre-cut label releasably adhered thereto by changing the direction of motion of the carrier strip by 90.degree., guiding the partially separated label through rollers which propel the label forward causing it to separate from the carrier strip and maintain contact with a spring-loaded arm which forces the leading edge of the label into contact with the moving surface and causes the label to become progressively attached thereto. This method is not generally applicable to adhering labels to a stationary surface, does not provide means to compensate for relative motion between the label and the carrier strip during coiling and storage, and does not prevent contact between the adherent layer of the label and the surfaces of the label application equipment.
None of these prior art label application methods are adapted to the accurate production and placement of pressure-sensitive labels. There remains therefore a need for a practical method of sequentially producing a high quality unprinted or printed label from a continuous length of label stock, precisely locating the label relative to a transport means without contact between the adherent layer of the label and any component of the label application equipment, and accurately applying the label to the surface of a stationary product. A process incorporating these improvements would substantially reduce the cost of applying labels to a product, improve the quality of the applied label, and improve the appearance of the product containing the label.